In recent years, while communication demands based on a spread of the internet and the like are increased, a wavelength division multiplexing (WDM) system utilizing broadband characteristics of optical amplifiers is being widely used.
All or part of optical nodes are provided with an optical add-drop multiplexer (OADM) in the WDM system. The optical add-drop multiplexer can add an optical signal to an optical transmission line in units of wavelength and take out the optical signal from the optical transmission line in units of wavelength.
The optical add-drop multiplexer is provided with a function of adding an optical signal having a desired wavelength to a WDM optical signal (optical add function) and a function of dropping the optical signal having the desired wavelength from the WDM optical signal (optical drop function). The optical add-drop multiplexer that adds and/or drops the optical signal having the desirable wavelength may be referred to as ROADM (Reconfigurable OADM).
The optical add-drop multiplexer preferably has a CDC (Colorless, Directionless, and Contentionless) function so that it is possible to flexibly set or modify a wavelength path.
Colorless represents a configuration or a function with which an arbitrary wavelength can be input to an arbitrary port of the optical add-drop multiplexer, and an arbitrary wavelength can be output from an arbitrary port. Directionless represents a configuration or a function with which optical signals from respective terminal stations can be guided to arbitrary routes, and the optical signals from the respective arbitrary routes can be guided to arbitrary terminal stations in a configuration where the optical add-drop multiplexer includes plural routes. Contentionless represents a configuration or a function with which a collision of optical signals having a same wavelength is avoided in the optical add-drop multiplexer.
Japanese Laid-open Patent Publication No. 2012-015726 discloses an example of the optical add-drop multiplexer having the CDC function, for example.
Manufacturing costs for the optical add-drop multiplexer are preferably low. In addition to the optical add-drop multiplexer, manufacturing costs for various types of optical modules, an optical apparatus, an optical system, and the like are preferably as low as possible.
However, as the number of optical devices (optical elements, for example) included in the optical add-drop multiplexer, the various types of optical modules, the optical system, and the like is higher, the manufacturing costs are generally higher. As the number of relatively expensive optical devices such as an optical channel monitor (OCM) is higher, the manufacturing costs are higher. If more types of optical modules included in the optical add-drop multiplexer, the optical system, and the like are used, the manufacturing costs are higher.